EP1245972A2 - Optische Faser, optische Übertragungsstrecke mit dieser optischen Faser, und optisches Übertragungssystem - Google Patents

Optische Faser, optische Übertragungsstrecke mit dieser optischen Faser, und optisches Übertragungssystem Download PDF

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Publication number
EP1245972A2
EP1245972A2 EP02252400A EP02252400A EP1245972A2 EP 1245972 A2 EP1245972 A2 EP 1245972A2 EP 02252400 A EP02252400 A EP 02252400A EP 02252400 A EP02252400 A EP 02252400A EP 1245972 A2 EP1245972 A2 EP 1245972A2
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Prior art keywords
optical fiber
glass layer
refractive index
wavelength
less
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French (fr)
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EP1245972A3 (de
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Naomi Kumano
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Furukawa Electric Co Ltd
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Furukawa Electric Co Ltd
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02004—Optical fibres with cladding with or without a coating characterised by the core effective area or mode field radius
    • G02B6/02009—Large effective area or mode field radius, e.g. to reduce nonlinear effects in single mode fibres
    • G02B6/02014—Effective area greater than 60 square microns in the C band, i.e. 1530-1565 nm
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02214—Optical fibres with cladding with or without a coating tailored to obtain the desired dispersion, e.g. dispersion shifted, dispersion flattened
    • G02B6/02219—Characterised by the wavelength dispersion properties in the silica low loss window around 1550 nm, i.e. S, C, L and U bands from 1460-1675 nm
    • G02B6/02228—Dispersion flattened fibres, i.e. having a low dispersion variation over an extended wavelength range
    • G02B6/02238—Low dispersion slope fibres
    • G02B6/02242—Low dispersion slope fibres having a dispersion slope <0.06 ps/km/nm2
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02214—Optical fibres with cladding with or without a coating tailored to obtain the desired dispersion, e.g. dispersion shifted, dispersion flattened
    • G02B6/02219—Characterised by the wavelength dispersion properties in the silica low loss window around 1550 nm, i.e. S, C, L and U bands from 1460-1675 nm
    • G02B6/02266—Positive dispersion fibres at 1550 nm
    • G02B6/02271—Non-zero dispersion shifted fibres, i.e. having a small positive dispersion at 1550 nm, e.g. ITU-T G.655 dispersion between 1.0 to 10 ps/nm.km for avoiding nonlinear effects
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/028—Optical fibres with cladding with or without a coating with core or cladding having graded refractive index
    • G02B6/0281—Graded index region forming part of the central core segment, e.g. alpha profile, triangular, trapezoidal core
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
    • G02B6/03616—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference
    • G02B6/03638—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 3 layers only
    • G02B6/03644—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 3 layers only arranged - + -
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
    • G02B6/03616—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference
    • G02B6/03688—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 5 or more layers

Definitions

  • the present invention relates to an optical fiber used for optical transmission such as wavelength division multiplexing transmission or the like in a wavelength band of 1.5 ⁇ m, an optical transmission line using the optical fiber, and an optical transmission system.
  • WDM wavelength division multiplexing
  • TDM time division multiplexing
  • the wavelength division multiplexing transmission is carried out in a wavelength band of 1.55 ⁇ m which corresponds to a gain band of an erbium-doped optical fiber amplifier (EDFA).
  • the wavelength band of 1.55 ⁇ m is a wavelength band having a center wavelength of 1550nm like a wavelength band from 1530nm to 1570nm.
  • the present invention is to provide an optical fiber having the following construction and an optical transmission line using the optical fiber, and an optical transmission system.
  • An optical fiber according to the present invention is characterized in that the chromatic dispersion value thereof at a wavelength of 1.55 ⁇ m is set to a value in the range of 4ps/nm/km to 10ps/nm/km and the cutoff wavelength thereof is set to a value in the range of 1.3 to 1.4 ⁇ m.
  • the dispersion slope of the optical fiber for the WDM transmission is large, the difference of chromatic dispersion between each channel is increased and therefore large-capacity and high bit rate communications can not be obtained. Conversely, if the dispersion slope of the optical fiber for the WDM transmission can be reduced, the difference of chromatic dispersion between each channel can be suppressed. Accordingly, the reduction of the dispersion slope is an indispensable factor for the large-capacity and high bit-rate communications.
  • the reduction of the dispersion slope generally causes reduction of an effective core area
  • the reduction of the effective core area causes a non-linear optical phenomenon due to interaction between each channel when the WDM transmission is carried out. That is, signal distortion ⁇ NL due to the non-linear optical phenomenon is generally represented by the following equation (1), and thus if the effective core area of the optical fiber is small, the signal distortion due to the non-linear optical phenomenon is intensified.
  • ⁇ NL (2 ⁇ x n 2 x L eff x P) / ( ⁇ x A eff )
  • ⁇ represents the ratio of the circumference of a circle to its diameter
  • n 2 represents a non-linear refractive index
  • L eff represents an effective optical fiber length
  • P represents the optical intensity of signal light
  • ⁇ represents a signal light wavelength
  • a eff represents an effective core area.
  • the dispersion slope is reduced while the cutoff wavelength is set to 1000nm and the effective core area is kept to about 55 ⁇ m 2 .
  • This optical fiber has an excellently balanced characteristic as described above, however, the reduction of the dispersion slope is limited to about 0.045ps/nm 2 /km .
  • the 1.5 ⁇ m wavelength band is such a wavelength band as located in the wavelength range of 1460nm to 1650nm, and the term of the 1.5 ⁇ m wavelength band will be used in this sense.
  • the Raman fiber amplifier is about to be practically used.
  • the Raman fiber amplifier uses a phenomenon that a gain appears at a longer wavelength side shifted from the wavelength of pumping light by about 100nm by the stimulated Raman scattering which occurs when strong light (pumping light) is incident to an optical fiber.
  • the Raman amplification is a method of irradiating signal light in a wavelength band having the gain to the optical fiber thus stimulated to thereby amplify the signal light.
  • the WDM transmission using the Raman amplification technique is carried out by inputting pumping light at a wavelength side shorter than the wavelength of signal light by about 100nm.
  • the WDM transmission is carried out by using signal light in the 1.55 ⁇ m wavelength band, there is a case where pumping light having a wavelength of 1.42 ⁇ m (shortest wavelength) is incident to an optical fiber.
  • NZ-DSF non-zero dispersion shifted optical fiber
  • the NZ-DSF has a chromatic dispersion of about +4ps/nm/km at a wavelength of 1.55 ⁇ m, and also has a dispersion slope of 0.045ps/nm 2 /km or more at the same wavelength. Accordingly, the zero dispersion wavelength of the NZ-DSF is equal to about 1.45 ⁇ m.
  • the conventional NZ-DSF has a problem that when pumping light of 1.42 ⁇ m in wavelength, for example, is incident to an optical fiber, interference based on four-wave mixing or the like occurs because the pumping light wavelength and the zero dispersion wavelength are very close to each other. Even if the NZ-DSF is applied to the WDM transmission of the 1.55 ⁇ m wavelength band by using the Raman fiber amplifier, exelent performance cannot be obtained unless this problem is solved.
  • the absolute value of the chromatic dispersion of a representative NZ-DSF at the wavelength of 1.55 ⁇ m is equal to about 4ps/nm/km, and the dispersion slope thereof is equal to 0.045ps/nm 2 /km or more. Since the NZ-DSF has such a chromatic dispersion characteristic, a dispersion-compensating optical fiber (DCF) used to compensate the dispersion and the dispersion slope is required to have a high dispersion compensation rate (a dispersion slope having a high absolute value).
  • DCF dispersion-compensating optical fiber
  • a dispersion compensator is considered as a module technique important to construct the WDM transmission system. If the design of DCF is difficult as described above, it disturbs construction of the WDM transmission system.
  • DCF for the NZ-DSF has been recently actively studied in learned societies such as OFC2000/TuG4, etc., and an optical fiber used to compensate the dispersion and the dispersion slope will be described hereunder.
  • Dispersion compensate rate(%) ⁇ (dispersion slope DSCF / dispersion slope DSF ) / (dispersion value DSCF ) / (dispersion value DSF ) ⁇ x 100
  • the dispersion slope DSCF indicates the dispersion slope of the DCF
  • the dispersion slope DSF represents the dispersion slope of an optical fiber (non-zero dispersion shifted optical fiber: NZ-DSF) for a transmission line to which dispersion compensation is aplied
  • the dispersion value DSCF indicates the dispersion value of the DCF
  • the dispersion DSF indicates the dispersion value of the optical fiber for the transmission line.
  • the chromatic dispersion in a broad wavelength band can be compensated more entirely. That is, as the dispersion compensate rate is closer to 100%, the chromatic dispersion of the overall optical line can be close to substantially zero in the broad wavelength band.
  • DPS dispersion/dispersion slope
  • the chromatic dispersion and the dispersion slope of the optical fiber for the transmission line can be more compensated in the broad wavelength band by the DCF.
  • the conventional optical fiber for the transmission path has small DPS, and as DPS of the DCF is reduced to the same level as DPS of the optical fiber for the transmission line, the bending loss characteristic is increased as shown in Fig. 5.
  • the bending loss value shown in Fig. 5 is measured at a diameter of 20mm ⁇ when light of 1.55 ⁇ m is incident.
  • the WDM transmission system using the conventional optical fiber for the transmission line needs a DCF having small DPS and small bending loss characteristic, and thus it is difficult to construct the system.
  • an optical fiber which can suppress the problems such as interference between pumping light and signal light, etc. and also suppress waveform distortion due to the chromatic dispersion even when the WDM transmission with Raman amplifiers in the 1.5 ⁇ m wavelength band is carried out, and is suitably used for the WDM transmission.
  • an optical fiber which can compensate the chromatic dispersion by using a DCF having low non-linearity, a low dispersion slope and a small bending loss .
  • optical transmission line and the optical transmission system according to the present invention are suitably used for the WDM transmission, for example, in the 1.5 ⁇ m wavelength band with making the best use of the advantage of the optical fiber.
  • Fig. 1A shows a refractive index distribution profile of a first embodiment of an optical fiber according to the present invention.
  • Fig. 1B shows the cross-sectional construction of the optical fiber of Fig. 1A
  • Various refractive index profiles may be used as the profile of the refractive index distribution of the optical fiber according to the present invention.
  • a refractive index profile as shown in Fig. 1A which is relatively simple in structure and easy to be designed and manufactured, is used.
  • the optical fiber according to the first embodiment has multi-layered glass layers having different compositions between neighboring layers.
  • the optical fiber has a four-layered glass layer, and the four-layered glass layer comprises a first glass layer 1, a second glass layer 2, a third glass layer 3 and a standard layer 6. These glass layers are formed concentrically as shown in Fig. 1B.
  • the standard layer 6 is a layer (clad layer) serving as a standard of the refractive index distribution in the four glass layers. Inside the standard layer 6 are formed the three glass layers (core glass layer) of the first glass layer 1, the second glass layer 2 and the third glass layer 3.
  • the maximum refractive index of the first glass layer 1 formed at the innermost of the optical fiber and the maximum refractive index of the third glass layer 3 formed at the third layer position from the innermost of the optical fiber are set to be higher than the refractive index of the standard layer 6.
  • the minimum refractive index of the second glass layer 2 formed at the second layer position from the innermost of the optical fiber is set to be lower than the refractive index of the standard layer 6.
  • the refractive index distribution shape of the first glass layer 1 exhibits ⁇ (alpha) -profile.
  • the optical fiber of the first embodiment is designed so that ⁇ 1 > ⁇ 2 > ⁇ 3 is satisfied when the maximum relative refractive index difference of the first glass layer 1 from the standard layer 6 is represented by ⁇ 1, the minimum relative refractive index difference of the second glass layer 2 from the standard layer 6 is represented by ⁇ 2, and the maximum relative refractive index difference of the third glass layer 3 from the standard layer 6 is represented by ⁇ 3.
  • each of the relative refractive index differences ⁇ 1, ⁇ 2, ⁇ 3 are defined by the following equations (3) to (5).
  • n 1 represents the maximum refractive index of the first glass layer
  • n 2 represents the maximum refractive index of the second glass layer
  • n 3 represents the maximum refractive index of the third glass layer.
  • ⁇ 1 ⁇ (n 1 2 - n 6 2 ) / 2n 6 2 ⁇ x
  • ⁇ 2 ⁇ (n 2 2 - n 6 2 ) / 2n 6 2 ⁇ x
  • ⁇ 3 ⁇ (n 3 2 - n 6 2 ) / 2n 6 2 ⁇ x 100
  • the diameter of the first glass layer 1 is represented by a
  • the diameter of the second glass layer 2 is represented by b
  • the diameter of the third glass layer 3 is represented by c.
  • the inventor of this application has made simulations by using as parameters the relative refractive index differences ⁇ 1, ⁇ 2, ⁇ 3, a constant ⁇ and the ratio of the diameter a of the first glass layer 1, the diameter b of the second glass layer and the diameter c of the third glass layer 3, and determined the optimum refractive index profile of the optical fiber of the first embodiment.
  • the simulation condition was set so that the cutoff wavelength of the optical fiber was set in the range of 1.3 ⁇ m to 1.4 ⁇ m, and the dispersion slope (the average value of the dispersion slope) at the wavelength of 1.55 ⁇ m in the 1.5 ⁇ m wavelength band was set to a positive value of 0.035ps/nm 2 /km or less. Further, the inventor of this application determined the optimum refractive index profile of the first embodiment on the basis of the relationship between the effective core area and the bending loss within this range. In this specification, the cutoff wavelength is measured for an optical fiber of 2m in length.
  • the relative refractive index difference ⁇ 1 is set to 0.7% or less. Further, it has been also found that if the relative refractive index difference ⁇ 1 is set to a value less than 0.4%, the bending loss is increased to 5dB/m or more. Therefore, the relative refractive index difference ⁇ 1 is set to a value within the range of 0.4% to 0.7%.
  • the range of the relative refractive index difference ⁇ 2 is set to the range of -0.6% or more to -0.1% or less.
  • the diameter b of the second glass layer 2 is set to a value larger than the diameter a of the first glass layer 1 by more than 2.2 times, the dispersion slope is larger than 0.035ps/nm 2 /km. Still further, it has been also found that if the diameter b of the second glass layer 2 is set to a value smaller than the diameter a of the first glass layer 1 by 1.5 time, the effective core area is smaller than 40 ⁇ m 2 . Therefore, the diameter b of the second glass layer 2 is set to be 1.5 times or more to 2.2 times or less as large as the diameter a of the first glass layer 1. That is, the range of b/a is 1.5 to 2.2.
  • the relative refractive index difference ⁇ 3 is set to a value larger than 0.4%, the cutoff wavelength is larger than 1.4 ⁇ m. Further, it has been also found that if the relative refractive index difference ⁇ 3 is set to a value less than 0.05%, the dispersion slope is larger than 0.035ps/nm 2 /km. Therefore, the range of the relative refractive index difference ⁇ 3 is set to the range of 0.05% to 0.4%.
  • the diameter c of the third glass layer 3 is set to a value larger than 3.5 times the diameter a of the first glass layer 1, the cutoff wavelength is larger than 1.4 ⁇ m . Still further, it has been also found that if the diameter c of the third glass layer 3 is set to a value smaller than 2.2 times the diameter a of the first glass layer 1 , the dispersion slope is larger than 0.035ps/nm 2 /km. Therefore, the diameter c of the third glass layer 3 is set to be 2.2 times or more to 3.5 times or less as large as the diameter a of the first glass layer 1. That is, the range of c/a is set 2.2 to 3.5 .
  • the optical fiber of the first embodiment has the refractive index profile as described above, and the cutoff wavelength is set in the range of 1.3 ⁇ m to 1.4 ⁇ m.
  • the optical fiber of the first embodiment is designed so that the dispersion value at the wavelength of 1.55 ⁇ m is set in the range of 4ps/nm/km or more to 10ps/nm/km or less.
  • the optical fiber of the first embodiment is designed so that the dispersion slope in at least a predetermined wavelength region of the 1.55 ⁇ m wavelength band is set to a positive value of 0.035ps/nm 2 /km or less and the zero dispersion wavelength is set to 1.43 ⁇ m or less.
  • the optical fiber of the first embodiment is designed so that the effective core area in a predetermined wavelength region the 1.5 ⁇ m wavelength band is set in the range of 40 ⁇ m 2 or more to 60 ⁇ m 2 or less.
  • the optical fiber of the first embodiment is designed so that the bending loss at the diameter 20mm in the 1.5 ⁇ m wavelength band is set to 5dB/m or less and the polarization mode dispersion is set to 0.07ps/ ⁇ km or less.
  • the optical fiber of the first embodiment is constructed as described above and it has a cutoff wavelength of 1.3 ⁇ m or more, so that the bending loss at the diameter of 20mm ⁇ in the 1.5 ⁇ m wavelength band can be set to 5dB/m or less. That is, the optical fiber of the first embodiment has this construction, and thus even , the bending loss of the optical fibers in a optical cable can be reduced.
  • the cutoff wavelength of the optical fiber of the first embodiment is set to 1.4 ⁇ m or less, so that the single mode operation can be surely performed in not only the optical transmission at a wavelength of 1.55 ⁇ m , but also the optical transmission at a wavelength of 1.46 ⁇ m , and the WDM transmission in the 1.5 ⁇ m wavelength band can be carried out.
  • the zero dispersion wavelength of the optical fiber of the first embodiment is set to 1.43 ⁇ m or less, so that when Raman amplification is carried out in the 1.55 ⁇ m wavelength band, interference such as four-wave mixing with pumping light at a wavelength of about 1.4 ⁇ m can be suppressed.
  • the effective core area in at least a wavelength region (a wavelength band containing at least a wavelength of 1.55 ⁇ m ) of the 1.5 ⁇ m wavelength band is set to 40 ⁇ m 2 or more. That is, the effective core area of the optical fiber of the first embodiment is set to a value which is equal to or more than the effective core area of the conventional optical fiber for the WDM transmission. Therefore, even when a lumped Raman fiber amplifier is applied to the WDM transmission, distortion of signal light due to the non-linear phenomenon can be suppressed in the optical fiber of the first embodiment.
  • the Raman fiber amplifiers are classified into a distributed Raman fiber amplifier and a lumped Raman fiber amplifier.
  • the lumped Raman fiber amplifier is applied to the WDM transmission, the non-linear phenomenon in the optical fiber cannot be ignored.
  • the effective core area in at least a wavelength region of the 1.5 ⁇ m wavelength band is set to 40 ⁇ m 2 or more. Accordingly, by performing the WDM transmission in the wavelength band having the effective core area as described above, the distortion of the signal light can be suppressed.
  • the effective core area in at least a wavelength region (wavelength band containing at least a wavelength of 1.55 ⁇ m 1.55 ⁇ m ) of the 1.5 ⁇ m wavelength band is set to 60 ⁇ m 2 or less. Therefore, the optical fiber of the first embodiment can suppress the reduction of the efficiency of the Raman amplification by performing the WDM transmission using the Raman fiber amplifier in the wavelength band in which the effective core area can be obtained.
  • the dispersion value at the wavelength of 1.55 ⁇ m is set to 10ps/nm/km or less, so that the distortion due to the chromatic dispersion can be suppressed without large local chromatic dispersion.
  • the dispersion slope in the 1.55 ⁇ m wavelength and is set to a positive value of 0.035ps/nm 2 /km or less to reduce the absolute value of the dispersion slope. Therefore, the optical fiber of the first embodiment can reduce the difference of chromatic dispersion between each channel, so that signal deterioration , which occur when signal is transmitted in a otical fiber, can be prevented .
  • the optical fiber of the first embodiment is suitable for the WDM transmission in the 1.5 ⁇ m wavelength band to which the Raman fiber amplifier is applied.
  • the chromatic dispersion value at the wavelength of 1.55 ⁇ m is set to 4ps/nm/km or more, and the dispersion slope in at least a predetermined wavelength region of the 1.55 ⁇ m wavelength band is set to a positive value of 0.035ps/nm 2 /km or less to thereby increasing the value of DPS. Accordingly, the optical fiber of the first embodiment can compensate the dispersion slope by using a DCF having a small bending loss.
  • the optical fiber of the first embodiment has a small absolute value of the dispersion slope. Therefore, by connecting a conventional dispersion slope compensating optical fiber or the like to the optical fiber of this embodiment, the dispersion slope of the optical fiber can be easily compensated.
  • the polarization mode dispersion is set to 0.07ps/ ⁇ km or less, thereby avoiding the problem of polarization mode dispersion which occurs in high-speed transmission.
  • Table 1 shows a specific simulation result of the first embodiment having the refractive index profile shown in Fig. 1A.
  • This simulation was performed under the condition that the relative refractive index differences ⁇ 1, ⁇ 2, ⁇ 3 and the constant ⁇ , and the ratio of the diameter a of the first glass layer 1, the diameter b of the second glass layer 2 and the diameter c of the third glass layer 3 are set in the respective ranges as described above. Further, the inventor determined a refractive index profile with which the dispersion slope could be set to a positive value of 0.035ps/nm 2 /km or less and the zero dispersion wavelength is set to 1.43 ⁇ m or less while keeping the effective core area at the wavelength of 1.55 ⁇ m to about 45 ⁇ m 2 under the above condition.
  • Aeff indicates the effective core area when light at the wavelength of 1.55 ⁇ m propagates
  • ⁇ c indicates the cutoff wavelength at the length of 2m
  • bending indicates the value of the bending loss at the diameter of 20mm to light at the wavelength of 1.55 ⁇ m
  • ⁇ o indicates the zero dispersion wavelength.
  • Core diameter indicates the value of the diameter c of the third glass layer 3
  • PMD indicates the polarization mode dispersion.
  • the polarization mode dispersion is set to 0.07ps/ ⁇ km or less for each sample #1, #2.
  • the optical fiber having the refractive index profile having the three-layer structure shown in Fig. 1A can achieve the following values while the bending loss value at the diameter of 20mm to light at the wavelength of 1.55 ⁇ m is set to 5.0dB/m or less and the cutoff wavelength is set in the range of not less than 1.3 ⁇ m or more to 1.4 ⁇ m or less.
  • the average value of the dispersion slope in the 1.55 ⁇ m wavelength band can be set to 0.035ps/nm 2 /km or less
  • the zero dispersion wavelength can be set to 1.43 ⁇ m or less
  • the effective core area when light at the wavelength of 1.55 ⁇ m propagates can be set in the range of 40 ⁇ m 2 or more to 60 ⁇ m 2 or less.
  • the optical fiber having the refractive index profile which has the three-layered structure shown in Fig. 1A can achieve both of the low dispersion slope and the low non-linearity. Further, the optical fiber can suppress the interference such as four-wave mixing between Raman amplification pumping lights or the like to some degree even when the transmission in the 1.55 ⁇ m wavelength band is carried out by using the Raman amplifying technique because the zero dispersion wavelength ⁇ o is smaller than 1.43 ⁇ m (1430nm).
  • the inventor has found that at least one of characteristics was deteriorated when he made experiments to reduce the dispersion slope in the refractive index profile as shown in Fig. 1A in order to expanding the transmission wavelength band to a shorter wavelength region.
  • dispersion slope is set to a positive value of 0.025ps/nm 2 /km or less as indicated in the samples of the following table 2 (#3, #4), some characteristics are deteriorated.
  • the effective core area when light at the wavelength of 1.55 ⁇ m propagates is less than 40 ⁇ m 2 .
  • the cutoff wavelength is not within the range of 1.3 ⁇ m or more to 1.4 ⁇ m or less.
  • the inventor has made various studies to further expand the transmission wavelength band, particularly to a shorter wavelength region, and has proposed the construction of the following second embodiment of the optical fiber according to the present invention.
  • the optical fiber of the second embodiment has a refractive index profile shown in Fig. 2A, and also has a cross-sectional structure shown in Fig. 2B.
  • the optical fiber of the second embodiment has a first glass layer 1, a second glass layer 2 and a third glass layer 3 inside a standard layer 6.
  • the construction of the first to third glass layers 1 to 3 is substantially the same as the first embodiment.
  • a fourth glass layer 4 provided at the outer periphery of the third glass layer 3 and a fifth glass layer 5 provided at the outer periphery of the fourth glass layer 4 are formed between the third glass layer 3 and the standard layer 6.
  • the refractive index of the fourth glass layer 4 is equal to that of the standard layer 6, and the minimum refractive index of the fifth glass layer 5 is set to be lower than the refractive index of the standard layer 6.
  • each relative refractive index difference ⁇ 4, ⁇ 5 is defined by the following equation (6), (7).
  • n 4 represents the refractive index of the fourth glass layer
  • n 5 represents the minimum refractive index of the fifth glass layer
  • n 6 represents the refractive index of the standard layer.
  • ⁇ 5 ⁇ (n 5 2 - n 6 2 ) / 2n 6 2 ⁇ x 100
  • the inventor has found the following probability that the fourth glass layer having the same refractive index as the standard layer 6 is provided at the outer periphery of the third glass layer 3 and the fifth glass layer 5 having a refractive index smaller than the refractive index of the standard layer 6 is provided at the outer periphery of the fourth glass layer 4. That is, it has been found that there is a probability that this structure may have no great effect on the transmission characteristics such as the dispersion slope, the effective core area, etc. of the optical fiber having the refractive index profile which has the three-layered structure, and suppress only the cutoff wavelength to a small value.
  • the inventor has made the following studies based on the simulations so as to satisfy the condition that the dispersion slope is set to a positive value below 0.025ps/nm 2 /km (preferably, about 0.02ps/nm 2 /km) and the effective core area when light at the wavelength of 1.55 ⁇ m propagates is equal to 40 ⁇ m 2 or more and also set the cutoff wavelength in the range of 1.3 ⁇ m or more to 1.4 ⁇ m or less.
  • the inventor selected optical fibers having the refractive index profile which has the three-layered structure like the first embodiment in which the dispersion slope was equal to a positive value of 0.025ps/nm 2 /km or less and the effective core area when light at the wavelength of 1.55 ⁇ m propagates was equal to 40 ⁇ m 2 or more.
  • the inventor set the parameters of the first, second and third glass layers 1, 2 and 3 to fixed values, and variously varied the diameter d of the fourth glass layer 4, the diameter e of the fifth glass layer 5 and the relative refractive index difference ⁇ 5 of the fifth glass layer 5 from the standard layer 6 to set the cutoff wavelength in the range of 1.3 ⁇ m or more to 1.4 ⁇ m or less.
  • the inventor made the following verification with the simulation.
  • the refractive index profile has a three-layered structure when no fifth glass layer 5 exists. Accordingly, by comparing the simulation in the three-layered structure and the simulation in the five-layered structure, variation of the cutoff wavelength due to the presence of the fifth glass layer 5 can be found.
  • the optical fiber having the refractive index profile which has the three-layered structure there were selected some index profiles with which the effective core area was equal to 40 ⁇ m 2 or more and the dispersion slope was equal to 0.025ps/nm 2 /km or less although the cutoff wavelength was larger than 1.40 ⁇ m.
  • the inventor made the simulation in the five-layered structure which was based on the three-layered structure having these index profiles.
  • the fourth glass layer 4 has the same refractive index as the standard layer 6, and the fifth glass layer 5 has a refractive index lower than the standard layer 6.
  • the inventor set the parameters of the first to third glass layers 1 to 3 to fixed values, and variously varied the diameter d of the fourth glass layer 4, the diameter e of the fifth glass layer 5 and the relative refractive index difference ⁇ 5 of the fifth glass layer 5 to search the optimal index profile. Further, by comparing the result of the simulation for the five-layered structure with the result of the simulation for the three-layered structure, the inventor selected, as the optimal index profile, a index profile that had no great effect on both of the dispersion slope and the effective core area and had an effect of reducing the cutoff wavelength.
  • the diameter d of the fourth glass layer 4 is set to a value smaller than 3.5 times the diameter a of the first glass layer 1, the dispersion slope would be larger than 0.025ps/nm 2 /km. Further it has been also found that if the diameter d of the fourth glass layer 4 is set to a value larger than 6.5 times the diameter a of the first glass layer 1 , the cutoff wavelength would be larger than 1.55 ⁇ m. Therefore, the diameter d of the fourth glass layer 4 is set to be 3.5 times or more to 6.5 times or less as large as the diameter a of the first glass layer 1.
  • the refractive index of the fourth glass layer 4 is set to the same refractive index as the standard layer 6.
  • the relative refractive index difference ⁇ 5 is set to -0.6% or less, the effect is saturated and there is such a tendency that the dispersion slope increases little by little.
  • the relative refractive index difference ⁇ 5 is set to be larger than -0.1%, the cutoff wavelength is larger than 1.55 ⁇ m. Therefore, the relative refractive index difference ⁇ 5 is set in the range of -0.6% or more to -0.1% or less.
  • the diameter e of the fifth glass layer 5 is set to a value smaller than 5.5 times the diameter a of the first glass layer 1 , the chromatic dispersion value is smaller than 4ps/nm/km, and also it has been found that if the diameter e of the fifth glass layer 5 is set to a value smaller than 7.0 times the diameter a of the first glass layer 1 , the dispersion slope is larger than 0.025ps/nm 2 /km. Therefore, the diameter e of the fifth glass layer 5 is set to be 5.5 times or more to 7.0 times or less as large as the diameter a of the first glass layer 1. That is, the range of e/a is set of 5.5 to 7.0.
  • the diameter e of the fifth glass layer 5 is set a value smaller than 1.02 times the diameter d of the fourth glass layer 4 , the effect of reducing the cutoff wavelength is lowered. Further, it has been also found that if the diameter e of the fifth glass layer is set to a value larger than 2.0 times the diameter d of the fourth glass layer 4 , the bending loss is increased. Therefore, the diameter e of the fifth glass layer 5 is set to be 1.02 times or more to 2.0 times or less as large as the diameter d of the fourth glass layer 4. That is, the range of e/d is set of 1.02 to 2.0.
  • the inventor has confirmed through the above verifications that the optical fiber having the fourth and fifth glass layer 4 and 5 can have the cutoff wavelength shifted to a shorter wavelength side (i.e., roughly by 0.15 ⁇ m to 0.30 ⁇ m) as compared with the optical fiber having the three-layered structure .
  • the optical fiber of the second embodiment is the optical fiber having refractive index profile of the five-layered structure, which has been determined on the basis of the above verifications.
  • the chromatic dispersion value at the wavelength of 1.55 ⁇ m is set to 4ps/nm/km or more and the cutoff wavelength is set in the range of 1.3 or more to 1.4 ⁇ m or less.
  • the dispersion slope in at least a predetermined wavelength region of the 1.55 ⁇ m wavelength band is set to a positive value of 0.025ps/nm 2 /km or less and the zero dispersion wavelength is set to 1.40 ⁇ m or less.
  • the other characteristics of the second embodiment except the dispersion slope and the zero dispersion wavelength are set to the same as the first embodiment, so that the same effect as the first embodiment can be achieved.
  • the dispersion slope at at least a predetermined wavelength region of the 1.55 ⁇ m wavelength band is set to a positive value of 0.025ps/nm 2 /km or less and the zero dispersion wavelength is set to 1.40 ⁇ m or less. Therefore, according to the second embodiment, when the Raman amplification is carried out in not only the 1.55 ⁇ m wavelength band, but also a wider wavelength band of 1.5 ⁇ m wavelength band , the interference such as four-wave mixing between pumping lights, etc. can be surely suppressed.
  • Tables 3A and 3B show a simulation result of the second embodiment having the refractive index profile shown in Fig. 2A.
  • the optical fiber having the refractive index profile which had the five-layered structure shown in Fig. 2A had the same effect as the first embodiment, and further the average value of the dispersion slope in the 1.55 ⁇ m wavelength band could be set to 0.025ps/nm 2 /km or less and the zero dispersion wavelength could be set to 1.40 ⁇ m or less.
  • Tables 4A and 4B show the characteristics, etc. of a prototype A formed on the basis of the design of the optical fiber of the sample #2 in the table 1 and a prototype B formed on the basis of the design of the optical fiber of the sample #6 in the tables 3A and 3B.
  • a characteristic line a in Fig. 3 indicates the chromatic dispersion characteristic of the optical fiber of the prototype A
  • a characteristic line b in Fig. 3 indicates the chromatic dispersion characteristic of the optical fiber of the prototype B.
  • each of these prototype optical fibers A and B has low chromatic dispersion and a low dispersion slope, and also has a low bending loss.
  • the zero dispersion wavelength of the prototype A is equal to 1407nm
  • the zero dispersion wavelength of the prototype B is equal to 1346nm.
  • the zero dispersion wavelengths of these prototypes A and B are equal to about 1400nm or to 1400nm or less, so that the problem of occurrence of the interference between pumping lights can be prevented when the WDM transmission in the 1.5 ⁇ m wavelength band is carried out by using Raman amplifiers.
  • each of the optical fibers of the prototypes A and B has an effective core area of 40 ⁇ m 2 or more and it has low transmission loss and low polarization-dependence loss when light at the wavelength of 1.55 ⁇ m propagates therethrough.
  • each optical fiber of the prototypes A and B is suitable for the WDM transmission in the 1.5 ⁇ m wavelength band, and further it has excellent compatibility with a DCF and a Raman amplifier.
  • a characteristic line b of Fig. 4 shows a chromatic dispersion characteristic of an example of the optical fiber according to the present invention
  • a characteristic a of Fig. 4 shows a chromatic dispersion characteristic when a conventional DCF having a chromatic dispersion characteristic shown by a characteristic line c of Fig. 4 is connected to the optical fiber of the present invention.
  • the dispersion slope of the optical fiber having the characteristic shown by the characteristic line b can be easily compensated by the conventional DCF. Accordingly, the chromatic dispersion in the wide wavelength band of 1.5 ⁇ m wavelength band can be substantially set to zero by using the optical fiber of the present invention as an optical fiber for transmission and compensating the dispersion slope with a conventional DCF.
  • the optical fiber of the present invention may have a refractive index profile other than the refractive index of the above-described embodiments. It is sufficient to design the optical fiber of the present invention so that the dispersion value at the wavelength of 1.55 ⁇ m is set in the range of 4ps/nm/km or more to 10ps/nm/km or less and the cutoff wavelength is set in the range of 1.3 or more to 1.4 ⁇ m or less as indispensable factors.
  • the effective core area, the chromatic dispersion value and the dispersion slope at least a predetermined wabelength region of the 1.5 ⁇ m wavelength band are set to proper values, and the zero dispersion wavelength is set to 1.4 ⁇ m or less, whereby an optical fiber which can perform the WDM transmission in the 1.5 ⁇ m wavelength band using a Raman amplifier with high quality and also an optical transmission system using the optical fiber can be constructed.
  • optical fiber which can perform the WDM transmission in the 1.55 ⁇ m wavelength band using the Raman amplifier with high quality while suppressing the four-wave mixing, and also an optical transmission system using the optical fiber.
  • the optical fiber and the optical transmission system are applied to the WDM transmission in the 1.5 ⁇ m wavelength band using the Raman amplifier.
  • the optical fiber and the optical transmission system of the present invention may be applied to the WDM transmission using an erbium-doped optical fiber amplifier.
  • the present invention may be applied to the WDM transmission in not only the 1.5 ⁇ m wavelength band, but also in other wavelength bands by modifying the construction of the optical fiber.

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  • Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Dispersion Chemistry (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Communication System (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
  • Optical Fibers, Optical Fiber Cores, And Optical Fiber Bundles (AREA)
  • Lasers (AREA)
  • Manufacture, Treatment Of Glass Fibers (AREA)
EP02252400A 2001-03-30 2002-04-02 Optische Faser, optische Übertragungsstrecke mit dieser optischen Faser, und optisches Übertragungssystem Withdrawn EP1245972A3 (de)

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JP2001100422 2001-03-30
JP2001100422A JP4443788B2 (ja) 2001-03-30 2001-03-30 光ファイバおよびその光ファイバを用いた光通信システム

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JP2002296441A (ja) 2002-10-09
JP4443788B2 (ja) 2010-03-31
EP1245972A3 (de) 2004-11-03
US20030021562A1 (en) 2003-01-30
CN1300608C (zh) 2007-02-14
CN1379253A (zh) 2002-11-13
US6768848B2 (en) 2004-07-27

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